jdc
Well-Known Member
that's a good time!
Coo I wish my crew could do 2000m in 5:30! (but then again we're only Vet D gimmers nowadays).
But what I was saying was that the normal analyses methods of seperating viscous and wave drag and guesstimating Cv and Cw from Reynolds and Froude numbers do apply despite the extreme aspect ratio. I wasn't saying that 1.34 * sqrt(L) holds.
In fact I dislike the concept of a 'hull limit' because it's obviously not zero resistance until this threshld then infinite above that - it's a curve where the friction is approximately a sqare law and the wave approximately an exponential, as I tried to illustrate in an earlier post.
A bit of drift, but I _think_ that with viiis there may be several reasons that longer hulls don't really help one go faster:
1. the formula for wave resistance as a funtion of length and speed doesn't hold in shallow water (where shallow is < ~LWL, clearly the case in nearly all rowing lakes and rivers;
2. one has to sit the damn thing, so some width and body is required; and
3. it has to be very stiff in torsion, and that's hard if the cross section is too small, ie beam is too low.
Coo I wish my crew could do 2000m in 5:30! (but then again we're only Vet D gimmers nowadays).
But what I was saying was that the normal analyses methods of seperating viscous and wave drag and guesstimating Cv and Cw from Reynolds and Froude numbers do apply despite the extreme aspect ratio. I wasn't saying that 1.34 * sqrt(L) holds.
In fact I dislike the concept of a 'hull limit' because it's obviously not zero resistance until this threshld then infinite above that - it's a curve where the friction is approximately a sqare law and the wave approximately an exponential, as I tried to illustrate in an earlier post.
A bit of drift, but I _think_ that with viiis there may be several reasons that longer hulls don't really help one go faster:
1. the formula for wave resistance as a funtion of length and speed doesn't hold in shallow water (where shallow is < ~LWL, clearly the case in nearly all rowing lakes and rivers;
2. one has to sit the damn thing, so some width and body is required; and
3. it has to be very stiff in torsion, and that's hard if the cross section is too small, ie beam is too low.